Switch devices are used in many applications to selectively provide electrical connections. In many cases, transistors are used as switches in such switch devices.
In many applications, for example for monitoring and/or diagnosis purposes, it is desirable or even required to perform measurements on the switch device, e.g. to monitor operation thereof. Typical measurements include for example current measurements measuring a load current through the switch device, voltage measurements measuring a voltage across the switch device or temperature measurements measuring a temperature of the switch device. This may for example be important in safety-critical applications to be able to detect an overcurrent, an overvoltage or an over-temperature and to take counter measures (like opening the switch) to avoid for example damages to the switch device due to such conditions.
Various approaches for current measurement are conventionally used in switch devices. For example, in some cases a shunt resistor has been used for current measurements. However, current measurements using a shunt resistor are comparatively expensive, as such a resistor needs to be designed for high currents requiring corresponding area on a chip and on the other hand the resistor has to be very precise (low tolerance regarding its resistance value) to enable an exact measurement. In particular, for switch devices switching a large range of currents (for example from some milliamperes up to some tens Ampere or more) designing and manufacturing a shunt resistor is a challenge for actual implementations. Moreover, the voltage drop over typical shunt resistors is usually quite low even for high currents (for example some microvolts), which makes measuring more difficult.
In other switch devices, a sense transistor is provided which may for example be coupled in a current mirror configuration to an actual switch transistor. Such sense transistors are a comparatively cheap solution for current measurements. However, with such sense resistors Measuring small currents may be a challenge due to a low voltage drop.
Yet other approaches measure a voltage between load terminals of the switch device as an indirect current measurement, for example between source and drain terminals of a switch transistor, which, however, creates similar challenges as the ones mentioned above. Furthermore, comparators or operational amplifiers are needed to evaluate a large voltage range.
Such comparator/operational amplifiers are also needed for measuring the voltage drop across typical switch devices, in particular when the switch devices are used for a large range of common mode voltages.
For temperature measurements, sometimes it is difficult to place a temperature sensor close enough to the switch device to provide precise temperature measurements.